1. Field of the Invention
The present invention relates to a field usable calibrator for humidity meters based on the use of a saturated salt solution.
2. Description of Related Art
The long-term stability of a humidity sensor and its electronic circuitry is influenced by, among other factors, its ambient temperature, humidity and contamination level, which all contribute to the periodical need for meter calibration. Calibration apparatuses capable of generating a known humidity at a known accuracy are available for calibration purposes. In general, the calibration apparatus is a container with a hole, into which the humidity meter is inserted for calibration. The container is air-tight, and an appropriate humidity level is obtained with the help of, for instance, a saturated salt solution, which covers the bottom of the container.
Methods based on the air-tight container and use of a saturated salt solution are relatively effective but during use, the drying and leaking of the salt solution as well as the contamination of humidity meter sensor can generate problems. Aqueous solutions of glycerin and sulfuric acid are also used for the generation of desired humidity, but the use of these substances is awkward due to their toxicity, and the risk of sensor contamination is high. The operation of the humidity meter can also be checked by wrapping the sensor into wetted paper, whereby a relative humidity of approximately 95% is attained after a certain time. The relative humidity level obtained with the help of this method is inaccurate and may lead to contamination or damaging of the sensor.